1. Field of the Invention
This invention relates to the field of high resiliency molded polyurethane foams. More particularly, it relates to improvement in strength properties of the foams by use of 2,3-dibromopropanol.
2. Description of the Prior Art
The use of 2,3-dibromopropanol, hereafter referred to as DBP, as a reactive flame retardant for polyurethane foams is well known in the art.
British Patent No. 895,966 discloses the use of DBP as a flame retardant with continued efficiency in flameproofing on accelerated aging. The foams described in this patent are rigid polyester foams. Nothing is disclosed regarding any other property effects with the exception of density. A further disclosure in British Patent No. 889,720 incorporates the use of antimony oxide for enhanced flame retardancy with DBP.
U.S. Pat. No. 3,772,222 relates to improvements in tear strength properties of high resiliency foams through the addition of halogenated phosphate esters such as tris(2,3-dibromoporopy) phosphate or by addition of certain plasticizers such as diethylphthalate or diisodecylphthalate. Reactive type flame retardant, such as DBP are not mentioned. Further, 4,4'-methylenebis (2-chloroanaline) is a necessary ingredient in the formulations disclosed.
U.S. Pat. No. 3,756,970 describes a process whereby compression set properties of a flexible foam are improved by the use of a combination of a halogen source (including DBP), a mineral acid, typical urethane catalysts, an undistilled phosgenation product of tolylene diamine, a polymeric polyol and a cross-linking agent.
Since DBP is a mono-functional alcohol, its incorporation into a foam formulation would not be expected to improve strength properties, rather it would be expected to weaken the foam and make it softer. Surprisingly it has been found that DBP used in a high resiliency foam formulation based on a blend of conventional and graft polyols using a blend of TDI and crude MDI as the isocyanate produces a foam with improved tensile and tear strength properties without significant softening of the foam. This is accomplished without further formulation modification. No cross-linker (as in the case of U.S. Pat. Nos. 3,772,222 or 3,756,970) or mineral acid is used.